Color photography



Patented May 25, 1954 UNITED 1.13'lAli-T.

OFFICE COLOR PHOTOGRAPHY No Drawing. Application February 6, 1951, Serial No. 209,710

Claims priority, application Great Britain February 9, 1950 3 Claims. 1

Processes of colour photography have already been proposed in which the integral tri-pack negative material used comprises three superimposed layers of emulsion, sensitive respectively to the three primary colours, supported upon a carrier with a thin stripping layer, or supplementary carrier, interposed between the uppermost layer-of emulsion and the other two layers of sensitive emulsion. The images developed in the lower two layers of emulsion are differentially coloured and are simultaneously or successively copied in one operation, after first removing the stripping layer bearing the uppermost layer of emulsion, the image developed in this uppermost layer of emulsion being copied in a separate operation.

In the previously proposed processes of this character, the copying of the image developed in the uppermost layer of emulsion is effected only after the stripping layer bearing that layer of emulsion has been stripped oh and transferred to another carrier or support. However, the transference of the layer of emulsion carried upon the stripping layer to another support in such a way that accurate registration of the three colour separation records can eventually be obtained is a matter of some practical difficulty, particularly in the case of cinematograph films.

In accordance with the present invention, this difficulty is avoided by copying the image developed in the uppermost layer of emulsion while it still remains superimposed upon the other two layers of emulsion on the original support. After copying, the stripping layer bearing this layer of emulsion can be stripped ofi and discarded, the other two layers of sensitive emulsion being then processed and copied as in the above mentioned process. The copying of the image in the uppermost layer of emulsion before stripping it off can be effected by a number of different methods, some of which are described below.

In all of these methods the integral tri-pack negative material used may comprise the following layers superimposed in the order named upon a Celluloid film or other suitable support: a

green-sensitive emulsion containing a colour forming substance, a red-sensitive emulsion containing a dilierent colour forming substance, a thin sheet of regenerated cellulose (constituting the stripping layer), a yellow filter layer and finally a blue-sensitive emulsion. The stripping layer may have its lower surface treated with a hydrophilic substance of low adhesive properties, such as calcium chloride solution, glycerine or other suitable material of a hygroscopic na- EXAMPLE I The negative material used is composed as described above with the top, blue-sensitive layer formed by a thin coating of unhardened emulsion. After exposure of the tri-pack, the top layer is developed in a tanning developer which gives penetration throughout the layer. A suitable developer is made up by mixing equal parts of the two following solutions:

Solution A Grams I-Iydroquino'ne 25 Potassium metabisulphite 6 Potassium bromide 25 Water to 1 litre.

Solution B Grams Potassium hydroxide 50 Water to 1 litre.

The time required for development is dependent upon the emulsion thickness. The tanning developer has the property of hardening the gelatine only in the silver image bearing areas. The unhardened gelatine can be removed by warm water or by treatment with potassium thiocyanate. After washing and drying the matrix so formed can be used to transfer a suitable dye (e. g. a pinatype dye) onto a transparent support. The colour of the dye may be yellow, orange or red and the blue separation colour record thus obtained is printed with blue light. After transference is complete the top layer is stripped off and discarded. If more than one transferred image is required, the matrix may be redyed before stripping.

EXAMPLE II image in the top layer. It is then fixed in alumfree hypo, washed and bleached with bichromate by first treating with a solution made up as follows:

Parts 10% solution of copper sulphate 19 10% solution of potassium bromide l and then with a solution made up as follows:

Parts 10% solution of potassium bromide 2 1% solution of potassium bichromate 1 Water to make 10 parts.

until image is completely bleached which takes about 4 minutes. The negative is-then washed thorough, treated with 1% sulphuric acid and again washed. The silver halide is then removed with plain hypo and the negative is washed and dried. The resulting matrix will have the imagebearing areas in hardened gelatine and can be used to transfer suitable dyes to another support, as in Example I.

EXAMPLE III The negative material used is similar to that of Examples I and II except that the top layer is a coating of hardened emulsion of normal thickness. After exposure, the top layer is developed normally, fixed, washed and bleached with a hydrogen peroxide solution, made up as under:

Parts Hydrogen peroxide 30 Copper sulphate 2 Nitric acid 5 Potassium bromide 0.5

Water to 1000 parts.

(See Wall, Practical Colour Photography, page 91.) The peroxide bleach removes the silver also the gelatine from the image-bearing areas, leaving a matrix which is reversed.

EXAMPLE IV The material used is the same as in Example III, but reversal of the matrix is avoided by processing the top layer of the exposed negative as follows. After developing normally and washing, it is bleached in acid bichromate or acid permanganate. The silver halide is then reexposed with light to which the other two emulsion layers of the negative are insensitive, or from which they are protected by filter layers. The top layer is then developed to completion and treated with peroxide bleach as in Example III.

The above examples are illustrative only and the method may be carried out in other ways also. For example, a matrix of a type similar to that obtained in Example II may be produced by the use of a uranium toning bath.

In another method of copying the image in the topmost layer of emulsion, this image is again converted to a gelatine matrix, but instead of using it to transfer dye onto a plain support it is used to transfer developer onto a blank photographic emulsion.

EXAMPLE V A gelatine matrix is produced in the top layer of emulsion, as in any one of Examples I to IV, and is then used to transfer a controlled amount of a developer solution onto a uniformly exposed blank emulsion supported on any suitable carrier. When the selective development of this emulsion has been completed, it is processed in the normal way to produce a silver image.

EXAMPLE VI As in Example V but the blank emulsion used for the copy is left unexposed and thiourea or methylene blue is added to the developer solution transferred onto it by the gelatine matrix.

In a third method, the image in the uppermost layer of emulsion is rendered light-reflecting relative to its background and is copied photographically onto a separate film, which is then processed in the normal manner to produce a silver image. To avoid fogging of the two lower emulsion layers of the negative material, blue light is used for copying the image in the top layer. Various methods are known for making the image stand out against its background and the following example sufiiciently illustrates this method of carrying out the invention.

After development of the topmost layer it is subjected to the action of one per cent solution of potassium iodide for a suitable period of time, Washed and dried. In this condition the topmost layer consists of a black and white silver image imbedded in a yellowish-white, opaque, silveriodide layer, suitable for printing by reflected light; such a process is indicated in U. S. specification No. 2,047,022.

A fourth method of carrying out the invention is based upon a process described in British patent specification No. 614,155 and elsewhere. In this process a film, after exposure in the camera, is developed in the usual way to give a negative image in silver. Without further treatment, such as washing or fixing, it is pressed into intimate contact with a second film under such conditions that the unreduced portions of the silver halide in the negative emulsion become transferred by diffusion to the second film and serve to form a positive image therein, while the reduced portions of the silver halide are left as a negative image in the first film. The positive material may be provided on its surface with a specially prepared layer, which may be gelatine and may contain a silver halide solvent such as sodium thiosulphate, together with an agent to develop silver halide which has not been exposed to light, such as stannous chloride, sodium arsenite and the like, and also an agent such as sodium sulphide which gives with the dissolved silver halides silver compounds which are with difliculty soluble in the gelatine layer. The nature of the reaction between silver negative image layer and positive forming layer is well-known.

EXAMPLE VIII The negative material used in carrying out the invention according to this fourth method may be composed as already described, with the distinction that the uppermost layer, in which the blue record is to be formed, consists of a very thin, dilute coating of silver halide emulsion. Such a layer has greater transparency than a normal layer of silver halide emulsion and this results in a greater effective overall speed to white light of the tri-pack film. This is of particular importance in colour photography carried out by means of a tri-pack or multilayer coating and represents a practical advance over the existing art.

After exposure in the camera the film is developed in a normal silver halide developer to give 5 a very thin image in silver. It is known that the copying processv here used. requires: only a socalled ghost image which would be totally unsuitable for printing a positive copy in theusual way, e. g. by light transmitted through the negative so formed.

After development and without further treatment of the film the tri-pack, which now bears the developed silver image in its topmost layer, is pressed into intimate contact with the positive forming layer carried on a separate support and is held in position for a suitable period. The duration of this period depends on the particular type of reaction involved between negative and positive, but may be up to several minutes. When the reaction is complete the two layers are separated and the positive image may then be after-treated as desired. It is known that the copying process here used secures an appreciable degree of intensification in the formation of the positiveimage, thus making after treatment of the positive image largely unnecessary.

The positive image being now carried on a separate support forms the master positive of the blue record of the tri-pack film and can be used to print ofi duplicate negatives in the usual way.

When the copying process is complete, the top layer of the tri-pack is stripped 01? and discarded. If necessary, however, the negative image in the topmost layer can be used again to form a second positive record in the way described.

Since the thickness of the topmost layer of the tri-pack can be very low, there is no absolute need to strip it oif after transferring the image in the way described, so that when this method of carrying out the invention is adopted the stripping layer may be omitted from between the two top layers of emulsion in the tri-pack negative material. It is, however, necessary to provide between these two layers a water permeable layer which carries the yellow filter substance required to effect the desired colour separation in the tri-pack. The combined thickness of the filter layer and of the topmost silver halide layer of the tri-pack is insufiicient to cause any appreciable loss of definition in subsequent printing of the bipack layer below the yellow filter layer.

To improve the transparency of the film the topmost layer and yellow filter layer can be bleached by suitable treatment to give substantially clear layers. To protect the bipack layer beneath the yellow filter layer from the developing agents which produce the silver negative image in the topmost layer the amount of developer solution taken-up must be controlled either in quantity or by increasing its viscosity by addition of suitable substances.

I claim:

1. A color photography process in which there is employed an integral tri-pack negative mate rial comprising a supporting carrier, a first layer of green-sensitive photographic emulsion containing a color forming substance superimposed upon said carrier, a second layer of red sensitive photographic emulsion containing a different color forming substance superimposed on said first layer of emulsion, a thin stripping layer superimposed on said second layer of emulsion, a yellow filter layer superimposed on said stripping layer and a third layer of blue-sensitive silver halide emulsion superimposed on said filter layer, said stripping layer having its surface in contact with said second layer of emulsion treated with a hydrophilic substance of low ad- 6 hesive properties and its surface in contact with said filter layer treated with a strongly adhesive solution, said process comprising the steps of developing a silver negative image. in said third layer of emulsion, transferring by diffusion to a positive material the unreduced silver halide contained in said third layer of emulsion and thereby forming a positive image in said positive material, separating said stripping layer together with said filter layer and said third layer of emulsion from said carrier and said first and second layers of emulsion and developing difierently colored images in said first and second layers of emulsion.

2. A color photography process in which after exposure in a camera of an integral tri-pack negative material comprising a supporting carrier, a first layer of emulsion sensitive to one of the primary colors and containing, a color forming substance, a second layer of emulsion sensitive to another of the primary colors and containing a different color forming substance and a third emulsion layer the same being a thin layer of dilute silver halide emulsion sensitive to the third primary color, said three layers of emulsion being superimposed upon said carrier in the order named, said negative material is treated to develop a thin silver negative image in said third layer of emulsion, said negative material is after development of said image and without further treatment applied to a positive material which comprises a gelatine layer containing a silver halide solvent, together with an agent to develop silver halide which has not been exposed to light, and an agent which gives with dissolved silver halide silver compounds which are with difiiculty soluble in the gelatine layer, so as to bring said third layer of emulsion into intimate contact with said gelatine layer, said intimate contact being maintained until a positive image corresponding to said negative image has been formed in said gelatine layer by the diffusion into it of unreduced silver halide from said third layer of emulsion, whereafter said negative and positive materials are separated and said negative material is treated to develop and fix difierently colored images in said first and second layers of emulsion and to bleach out said thin silver image from said first layer of emulsion.

3. A color photography process in which after exposure in a camera of an integral tri-pack negative material comprising a supporting carrier, a first layer and a second layer of emulsion,

' sensitive respectively to red and to green light and each containing a color forming substance, disposed in superimposed relation upon said carrier, a yellow filter layer superimposed on said layers of emulsion and a third emulsion layer the same being a thin layer of dilute silver halide emulsion sensitive to blue light superimposed on said filter layer, said negative material is treated to develop a thin silver negative image in said third layer of emulsion, said negative material is after development of said image and without further treatment applied to a positive material which comprises a gelatine layer containing a silver halide solvent, together with an agent to develop silver halide which has not been exposed to light, and an agent which gives with dissolved silver halide, silver compounds which are with diificulty soluble in the gelatine layer, so as to bring said third layer of emulsion into intimate contact with said gelatine layer, said intimate contact being maintained until a positive image corresponding to said negative image has been formed in said gelatine layer by the diffusion into it of unreduced silver halide from said third layer of emulsion, whereafter said negative and positive material are separated and said negative material is treated to develop and fix differently colored images in said first and second layers of emulsion and to bleach said third layer of emulsion and said filter to form substantially clear layers.

8 References Cited'in the fileof this patent UNITED STATES PATENTS Number Number Name Date Lage Sept. 4, 1928 Comstock Apr. 24, 1934 Webb Apr. 2, 1940 R0tt June 20, 1944 Coote Jan. 16, 1945 FOREIGN PATENTS Country Date Great Britain May 25, 1938 

1. A COLOR PHOTOGRAPHY PROCESS IN WHICH THERE IS EMPLOYED AN INTEGRAL TRI-PACK NEGATIVE MATERIAL COMPRISING A SUPPORTING CARRIER, A FIRST LAYER OF GREEN-SENSITIVE PHOTOGRAPHIC EMULSION CONTAINING A COLOR FORMING SUBSTANCE CUPERIMPOSED UPON SAID CARRIER, A SECOND LAYER OF RED SENSITIVE PHOTOGRAPHIC EMULSION CONTAINING A DIFFERENT COLOR FORMING SUBSTANCE SUPERIMPOSED ON SAID FIRST LAYER OF EMULSION, A THIN STRIPPING LAYER SUPERIMPOSED ON SAID SECOND LAYER OF EMULSION, A YELLOW FILTER LAYER SUPERIMPOSED ON SAID STRIPPING LAYER AND A THIRD LAYER OF BLUE-SENSITIVE SILVER HALIDE EMULSION SUPERIMPOSED ON SAID FILTER LAYER, SAID STRIPPING LAYER HAVING ITS SURFACE IN CONTACT WITH SAID SECOND LAYER OF EMULSION TREATED WITH A HYDROPHILIC SUBSTANCE OF LOW ADHESIVE PROPERTIES AND ITS SURFACE IN CONTACT WITH SAID FILTER LAYER TREATED WITH A STRONGLY ADHESIVE SOLUTION, SAID PROCESS COMPRISING THE STEPS OF DEVELOPING A SILVER NEGATIVE IMAGE IN SAID THIRD LAYER OF EMULSION, TRANSFERRING BY DIFFUSION TO A POSITIVE MATERIAL THE UNREDUCED SILVER HALIDE CONTAINED IN SAID THIRD LAYER OF EMULSION AND THEREBY FORMING A POSITIVE IMAGE IN SAID POSITIVE MATERIAL, SEPARATING SAID STRIPPING LAYER TOGETHER WITH SAID FILTER LAYER AND SAID THIRD LAYER OF EMULSION FROM SAID CARRIER AND SAID FIRST AND SECOND LAYER OF EMULSION AND DEVELOPING DIFFERENTLY COLORED IMAGES IN SAID FIRST AND SECOND LAYERS OF EMULSION. 